2010年6月23日 星期三
The issue of our enquiry
Our enquiry issue" How do tectonic activities affect Cheung chau's relief?" Generally the relief on Cheung chau island is quite low, the hihest point being formed in the north, about 107 metres above sea-levels. (#3) Tectonic activities in Cheung chau include vulcanicity (mainly intrusive) and faulting, and they can affect the relief of a place very much. Terefore in the following, we will discuss how do tectonic activities affect Cheung Chau's relief.
Photos' Captions
1. It is a dyke that Miss Leung had showed us. It is near the Cheung Po Tsai Cave. It is a quartz vein which is light in colour, some orange mosses are grow on its top surface.
2. We thought that it is the dyke, but Miss Leung told me that it may be the minerals which had deposited onto the rock. Is is a dyke or minerals? Yes, it is still a mystery!
3. The rock surface we shown is partly weathered and there are some mosses grow here.
4. Apen is placed on the faults of the rock in Nam Tam Wan in the South-eastern tip of Cheung chau.
5. This scenery shows the tectonic activities- well-jointed structures and external processes- weatherimg and erosion.
6. This photo shows massive joining, they are less resistance to weathering and erosion.
7. There is a diagonal line of pale pink coloured dyke. It was found in Nam Tam Wan in the Southern tip of Cheung chau.
8. This rock has undergone block disintergration, by thermal expansion and contraction.
9. This is an igneous rock found in Cheung chau. It contains three types of chemical minerals, including micas, feldspars and quartzes.
10. This photo shows honeycomb weathering by the removal of minerals in solution.
2. We thought that it is the dyke, but Miss Leung told me that it may be the minerals which had deposited onto the rock. Is is a dyke or minerals? Yes, it is still a mystery!
3. The rock surface we shown is partly weathered and there are some mosses grow here.
4. Apen is placed on the faults of the rock in Nam Tam Wan in the South-eastern tip of Cheung chau.
5. This scenery shows the tectonic activities- well-jointed structures and external processes- weatherimg and erosion.
6. This photo shows massive joining, they are less resistance to weathering and erosion.
7. There is a diagonal line of pale pink coloured dyke. It was found in Nam Tam Wan in the Southern tip of Cheung chau.
8. This rock has undergone block disintergration, by thermal expansion and contraction.
9. This is an igneous rock found in Cheung chau. It contains three types of chemical minerals, including micas, feldspars and quartzes.
10. This photo shows honeycomb weathering by the removal of minerals in solution.
References
1.
2. Ip Kim Wai, Lam Cji Chung, Sze Ming Hui, Wong Kam Fai, Yeung Kam Chuen. (2009) Senior Secondary 4 Exploring Geography Dynamic Earth. Hong Kong: Oxford University Press (China) Ltd
3. Topography. Retrieval 2010-05-02 from
http:// www.slcss.edu.hk/subjects/geog/cheungchau/topograp.htm
4. Hong Kong Gelogical Survery, Civil Engineering and Development Department. Weathering &Erosion- Introduction to Geomorphological Processes. Retrieval 2010-05-02 from
http://hkss.cedd.gov.hk/hkss/eng/education/GS/eng/hkg/chapter4.htm?tab=0
5. Queen's College by S.4E (group B) 2002-2003.Biological weathering. Retrieval 2010-05-02 from
http://www.qc.edu.hk/it-school/homepage/geog/cheung%20chau/web/phy.htm#honeycomb
6.
7.
http://www.hktraveler.com/greenteach/bio_01.htm
8. Rocks and Minerals (1996)
2. Ip Kim Wai, Lam Cji Chung, Sze Ming Hui, Wong Kam Fai, Yeung Kam Chuen. (2009) Senior Secondary 4 Exploring Geography Dynamic Earth. Hong Kong: Oxford University Press (China) Ltd
3. Topography. Retrieval 2010-05-02 from
http:// www.slcss.edu.hk/subjects/geog/cheungchau/topograp.htm
4. Hong Kong Gelogical Survery, Civil Engineering and Development Department. Weathering &Erosion- Introduction to Geomorphological Processes. Retrieval 2010-05-02 from
http://hkss.cedd.gov.hk/hkss/eng/education/GS/eng/hkg/chapter4.htm?tab=0
5. Queen's College by S.4E (group B) 2002-2003.Biological weathering. Retrieval 2010-05-02 from
http://www.qc.edu.hk/it-school/homepage/geog/cheung%20chau/web/phy.htm#honeycomb
6.
7.
http://www.hktraveler.com/greenteach/bio_01.htm
8. Rocks and Minerals (1996)
Attachment (Definition)
1. Mechanical weathering is the group of processes, such as frost wedging and volume changes of minerals, that result in the mechanical disruption of rocks, such as granular disintegration, exfoliation, joint block separation, shattering by changes in temperature or pressure.(#4)
2. Honeycomb weathering is the removal of minerals in solution produces a honeycombed effect on the rock face, this form of weathering is common in Cheung Chau, as Cheung Chau is along the caost where salt spray from the sea dissolves the minerals in the rocks.(#2)
3. Spheroidal weathering take place as water seeps joints, weathering works from the joints towards the interior of the rock. The unweathered corestone at the centre gets smaller and rounded as time goes by.(#2)
4. Biological weathering is the group of processes that are caused by the presence of vegetation, or to a lesser extent animal, including root wedging and the production of organic acids.(#4)
2. Honeycomb weathering is the removal of minerals in solution produces a honeycombed effect on the rock face, this form of weathering is common in Cheung Chau, as Cheung Chau is along the caost where salt spray from the sea dissolves the minerals in the rocks.(#2)
3. Spheroidal weathering take place as water seeps joints, weathering works from the joints towards the interior of the rock. The unweathered corestone at the centre gets smaller and rounded as time goes by.(#2)
4. Biological weathering is the group of processes that are caused by the presence of vegetation, or to a lesser extent animal, including root wedging and the production of organic acids.(#4)
Conclusion
There are tectonic activities included vuclanicity and faulting affect the relief of Cheung Chau. Nevertheless, weathering, erosion and mass movement also acts as the important role to shape and affect the relief of Cheung Chau as well. Last but not least, Cheung Chau's relief is low because of it's geology formation, i.e. granite, batholiths are shaped by internal and external factors.
Explanation and evaluation
First of all, there are mainly internal process include faulting and vulcanicity affect the relief of Cheung Chau.
In Nam Tam Wan, Southern tip of Cheung Chau, we can find that there is a pale pink dyke.(reference#3) But common dykes in Hong Kong are usually dark in colour. According to the book-Rocks and mineralsp. 30 (reference#10), it says that it is a granite dyke due to the solidification of cooled magma. It is paler than the surrounding granite bedrock because it may be the earlier dyke that appear on the ground and undergone serious weathering and erosion in hot and wet climate.
Referring to the map (reference#6), Cheung Chau is mainly formed by two granitic islands in the northern and southern part. Granite is a kind of intrusive igneous rocks. Which magmarises along the cracks to the earth's surface, then cools and solidies. During the cooling process, crystallized minerals group together and appear interlocking with each other. (reference#2). The three major minerals are quartz, mica and feldspar. Their size are relatively large and most of them are coarse-grained. Granite is an acidic rock, it has a high silica content. So theat its colour tends to be lighter. A batholith is a larger mass of intrusive rock formed deep underground. It is formed by the cooling of magmka that accumulates at a deep dome-shaped chamber. In Hong Kong, exposed batholiths cover over one-third of the area. They became exposed after the rocks on top were removed from erosion.
As granite is less resistant under hot and wet climate, it is therefore subject subject to serious weathering and erosion. Low hills with relatively gentle slopes and rounded peaks are formed. As I mentioned before, Cheung chau's relief is tend to be lower. Dykes and faults in Cheung Chau is mainly located at the southern and northern part of Cheung Chau.
Second, there are external process such as weathering, erosion and mass movement affect the relief of Cheung chau.
First of all, there are three types of weathering, which are mechanical weathering, chemical weathering and biological weathering.
We have found that mechanical weathering of block disintegration of rock in Cheung Chau, and it usually occurs in well-jointed rocks.
There are two forms of chemical weathering, which are honeycomb weathering and spheroidal weathering.
Let's take an example of honeycomb weathering , human head rock made up by quartz, feldspar and plagioclase. Among them, feldspar and plagioclase are the easiest to be eroded. Human head rocks formed by the process of honeycomb weathering, which is exposed in the open area and the coast, feldspar and plagioclase in the rock dissolved and carried away by rain water and the splashes of sea water or solution. Through all the year round with weathering and erosion, the shape and the arrangement of a small hole look like honeycomb.(#6)
In Cheung Chau, the notch inside may present many cracks. These cracks and joints are results of biological weathering. The roots of living plants may penetrate into the joints of well-jointed tock, causing them to enlarge. These roots on living plants may secret some organic acid, causing solution, hydration.(#5)
From above, there are mainly mechanical weathering and chemical weathering in Cheung Chau. In Cheung Chau field trip, there are many this types of rocks on the way. Moreover, mechanical weathering and chemical weathering usually work together and shaped the rock and the relief of a place efficiently.
Next, we would like to talk about water erosion and fluvial and coastal erosion in Cheung Chau.
Splashes of heavy rain can loose and move soil. During the rainy season, rainwater running down the wall of the cracks removes the soil grains, this thus formed rill erosion. When rill joins up and become deeper and wider channelss, gullies erosion is formed. Meamtime, gully erosion removes soil downslope, and itfinally lead to soil erosion. Furthermore, badland is formed if there with dense concentration of gullies.(#2) In Cheung Chau, they're found on the northern island.
Fluvial and coastal erosion refers to the erosion of rock materials from river banks and river bads. Along caost, erosion is brought about by waves and tides.(#2) For instant, there is a rock called turtle rock in Tung Wan Beach in Cheung Chau, which stays lonely in the sea of the beach.(#1)
From above, water erosion and fluvial and coastal erosion really pay an important role to shape the rock and the relief of Cheung Chau, because Cheung Chau is an offshore island, which means it is sounded by sea, and the rocks are easy eroded by waves and tide, etc. the examples are vase rock, seal rock and so on.
Finally, we would like to talk about mass movement include landslide and rockfalls in Cheung Chau.
Landslide is a kind of fast movement by which rocks and soils of all sizes collapse through either sliding or slumping along a curved surface.(#2)
Rockfalls refer to the free fall of rock fragments ranging from samll grains to huge blocks from steep or overhanging slopes. Partially weathered rocks may loose support and fall due to gravity. Rockfall is a sudden and very fast movement.(#2)
From above, we know that landslides and rockfalls are common phenomenon on slope. In 2006, there were landslides and rockfalls in Cheung Chau, and we can see that the preventive measures agencies there and so there were landslides taken in Cheung Chau. As the steeper the slope, the more serious the landslides and rockfalls, the higher the relief of a place. The more gentle the slope in Cheung Chau, the less serious the landslide and rockfalls, the lower the relief in Cheung Chau. As a result, we can prove that Cheung Chau's relief is quite low.
In Nam Tam Wan, Southern tip of Cheung Chau, we can find that there is a pale pink dyke.(reference#3) But common dykes in Hong Kong are usually dark in colour. According to the book-Rocks and mineralsp. 30 (reference#10), it says that it is a granite dyke due to the solidification of cooled magma. It is paler than the surrounding granite bedrock because it may be the earlier dyke that appear on the ground and undergone serious weathering and erosion in hot and wet climate.
Referring to the map (reference#6), Cheung Chau is mainly formed by two granitic islands in the northern and southern part. Granite is a kind of intrusive igneous rocks. Which magmarises along the cracks to the earth's surface, then cools and solidies. During the cooling process, crystallized minerals group together and appear interlocking with each other. (reference#2). The three major minerals are quartz, mica and feldspar. Their size are relatively large and most of them are coarse-grained. Granite is an acidic rock, it has a high silica content. So theat its colour tends to be lighter. A batholith is a larger mass of intrusive rock formed deep underground. It is formed by the cooling of magmka that accumulates at a deep dome-shaped chamber. In Hong Kong, exposed batholiths cover over one-third of the area. They became exposed after the rocks on top were removed from erosion.
As granite is less resistant under hot and wet climate, it is therefore subject subject to serious weathering and erosion. Low hills with relatively gentle slopes and rounded peaks are formed. As I mentioned before, Cheung chau's relief is tend to be lower. Dykes and faults in Cheung Chau is mainly located at the southern and northern part of Cheung Chau.
Second, there are external process such as weathering, erosion and mass movement affect the relief of Cheung chau.
First of all, there are three types of weathering, which are mechanical weathering, chemical weathering and biological weathering.
We have found that mechanical weathering of block disintegration of rock in Cheung Chau, and it usually occurs in well-jointed rocks.
There are two forms of chemical weathering, which are honeycomb weathering and spheroidal weathering.
Let's take an example of honeycomb weathering , human head rock made up by quartz, feldspar and plagioclase. Among them, feldspar and plagioclase are the easiest to be eroded. Human head rocks formed by the process of honeycomb weathering, which is exposed in the open area and the coast, feldspar and plagioclase in the rock dissolved and carried away by rain water and the splashes of sea water or solution. Through all the year round with weathering and erosion, the shape and the arrangement of a small hole look like honeycomb.(#6)
In Cheung Chau, the notch inside may present many cracks. These cracks and joints are results of biological weathering. The roots of living plants may penetrate into the joints of well-jointed tock, causing them to enlarge. These roots on living plants may secret some organic acid, causing solution, hydration.(#5)
From above, there are mainly mechanical weathering and chemical weathering in Cheung Chau. In Cheung Chau field trip, there are many this types of rocks on the way. Moreover, mechanical weathering and chemical weathering usually work together and shaped the rock and the relief of a place efficiently.
Next, we would like to talk about water erosion and fluvial and coastal erosion in Cheung Chau.
Splashes of heavy rain can loose and move soil. During the rainy season, rainwater running down the wall of the cracks removes the soil grains, this thus formed rill erosion. When rill joins up and become deeper and wider channelss, gullies erosion is formed. Meamtime, gully erosion removes soil downslope, and itfinally lead to soil erosion. Furthermore, badland is formed if there with dense concentration of gullies.(#2) In Cheung Chau, they're found on the northern island.
Fluvial and coastal erosion refers to the erosion of rock materials from river banks and river bads. Along caost, erosion is brought about by waves and tides.(#2) For instant, there is a rock called turtle rock in Tung Wan Beach in Cheung Chau, which stays lonely in the sea of the beach.(#1)
From above, water erosion and fluvial and coastal erosion really pay an important role to shape the rock and the relief of Cheung Chau, because Cheung Chau is an offshore island, which means it is sounded by sea, and the rocks are easy eroded by waves and tide, etc. the examples are vase rock, seal rock and so on.
Finally, we would like to talk about mass movement include landslide and rockfalls in Cheung Chau.
Landslide is a kind of fast movement by which rocks and soils of all sizes collapse through either sliding or slumping along a curved surface.(#2)
Rockfalls refer to the free fall of rock fragments ranging from samll grains to huge blocks from steep or overhanging slopes. Partially weathered rocks may loose support and fall due to gravity. Rockfall is a sudden and very fast movement.(#2)
From above, we know that landslides and rockfalls are common phenomenon on slope. In 2006, there were landslides and rockfalls in Cheung Chau, and we can see that the preventive measures agencies there and so there were landslides taken in Cheung Chau. As the steeper the slope, the more serious the landslides and rockfalls, the higher the relief of a place. The more gentle the slope in Cheung Chau, the less serious the landslide and rockfalls, the lower the relief in Cheung Chau. As a result, we can prove that Cheung Chau's relief is quite low.
Description
What are the internal process in Cheung Chau?
1. Faulting
There are three types of faults, which are normal (dip-slip) faults, reverse ( dip-slip ) faults, and strike-slip faults. There are minor faults in Cheung Chau.
2. Vulcanicity
There was mainly intrusive vulcanicity in Cheung Chau. Accordingto our textbook chapter1.3, magma enters cracks or chambers in the crust from asthenosphere. When magma cools and solidifies in the crust, it becomes a batholith, dyke,sill or laccolith. Batholith and dyke are mainly found in Hong Kong and Cheung Chau as well.
1. Faulting
There are three types of faults, which are normal (dip-slip) faults, reverse ( dip-slip ) faults, and strike-slip faults. There are minor faults in Cheung Chau.
2. Vulcanicity
There was mainly intrusive vulcanicity in Cheung Chau. Accordingto our textbook chapter1.3, magma enters cracks or chambers in the crust from asthenosphere. When magma cools and solidifies in the crust, it becomes a batholith, dyke,sill or laccolith. Batholith and dyke are mainly found in Hong Kong and Cheung Chau as well.
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